Polyvinylidene fluoride (PVDF) is a highly crystalline engineering thermoplastic offering an excellent combination of properties including but not limited to high chemical corrosion resistance, excellent abrasion resistance, high oxidative resistance and heat resistance. In addition, PVDF resins are unaffected by UV radiation, providing exceptional weathering resistance, have good light transmittance in films and are resistant to creep under mechanical stress. Another important property of PVDF resins is their inherent flame retardancy with low smoke generation during a fire event. PVDF resins can be used in many forms including but not limited to molded parts, extruded profiles, and as protective coatings.
Vinylidene fluoride is commonly copolymerized with comonomers such as hexafluoropropylene (HFP) to produce products having lower flexural modulus. Such PVDF copolymers, in general, have lower levels of crystallinity compared to homopolymers, with properties shifting as would be expected as crystallinity is reduced. In general, PVDF copolymers, such as copolymers with hexafluoropropylene (HFP), provide improvement in ductility and low temperature performance while maintaining much of the exceptional properties associated with PVDF resins. Unfortunately, the effects of HFP addition on improving low temperature ductility are limited. Vinylidene fluoride-HFP copolymers tend to have ductile-brittle transition temperatures (DBTTs) ranging between 0° C. and at best down to −15° C.
For many applications, a lower DBTT down to −40° C. or below is required, which is verified by performing impact tests at these low temperatures. Vinylidene fluoride-HFP copolymers as a class do not meet these low temperature impact requirements. In these cases, core shell impact modifiers (CSIMs) can be added to PVDF through various techniques to achieve low temperature performance. However, the addition of the traditional CSIMs to vinylidene fluoride-containing polymers compromises some of the excellent properties of these polymers. For example MBS modifiers with butadiene cores, while efficient in impact modification, have very poor weathering properties and oxidation resistance. All-acrylic impact modifiers compromise the flame properties of the vinylidene fluoride-containing polymer and are not as efficient as MBS based impact modifiers due to their relatively high core Tg.